1. Field of the Invention
The present invention relates to rangefinder devices. More specifically, the present invention relates to rangefinder devices for electro-active lenses.
2. Description of the Prior Art
Presbyopia is the loss of accommodation of the crystalline lens of the human eye that often accompanies aging. This loss of accommodation results in an inability to focus on near objects. The standard tools for correcting presbyopia are multi-focal spectacle lenses. A multi-focal lens is a lens that has more than one focal length (i.e. optical power) for correcting focusing problems across a range of distances. Multi-focal spectacle lenses work by means of a division of the lens's area into regions of different optical powers. Typically, a relatively large area located in the upper portion of the lens corrects for far distance vision errors, if any. A small area located in the bottom portion of the lens provides additional optical power for correcting near distance vision errors caused by presbyopia. A multifocal lens may also contain a small region located in the middle portion of the lens which provides additional optical power for correcting intermediate distance vision errors. Near distance is defined as being approximately 8″ to approximately 17″ from the wearer's eyes, intermediate distance is defined as being approximately 17″ to approximately 42″ from the wearer's eyes, and far distance is defined as being greater than approximately 42″ from the wearer's eyes.
The transition between the regions of different optical power may be either abrupt, as is the case for bifocal and trifocal lenses, or smooth and continuous, as is the case with progressive addition lenses. There are problems associated with these two approaches that can be objectionable to some patients. The visible line of demarcation associated with bifocals and trifocals can be aesthetically displeasing. Additionally, the abrupt change in optical power between regions may cause image jump. The smooth transition regions associated with progressive addition lenses cause unwanted astigmatism in the lens leading to blurred and distorted vision, which, in some patients, causes physical discomfort. Furthermore, in both approaches, the placement of the near vision correction area near the bottom edge of the lens requires patients to adopt a somewhat unnatural downward gaze for near vision tasks.
Electro-active lenses are an attractive alternative to conventional multifocal lenses. In an electro-active lens, an electro-active optical element may be embedded within or attached to an optical substrate. The optical substrate may be a finished, semi-finished or unfinished lens blank. When a semi-finished or unfinished lens blank is used, the lens blank may be finished during manufacturing of the lens to have one or more optical powers. An electro-active optical element may also be embedded within or attached to a conventional optical lens. The conventional optical lens may be a single focus lens or a multi-focal lens such as a progressive addition lens or a bifocal or trifocal lens. The electro-active optical element may be located in a portion or in the entire viewing area of the electro-active lens. The electro-active optical element may be spaced from the peripheral edge of the optical substrate for edging the electro-active lens for spectacles. The electro-active element may be located near the top, middle or bottom portion of the lens. When substantially no voltage is applied, the electro-active optical element may be in a deactivated state in which it provides substantially no optical power. In other words, when substantially no voltage is applied, the electro-active optical element may have the same refractive index as the optical substrate in which it is embedded. When voltage is applied, the electro-active optical element may be in an activated state in which it provides optical add power. In other words, when voltage is applied, the electro-active optical element may have a different refractive index than the optical substrate in which it is embedded.
Electro-active lenses may be used to correct for conventional or non-conventional errors of the eye. The correction may be created by the electro-active element, the conventional optical lens or by a combination of the two. Conventional errors of the eye include near-sightedness, far-sightedness, presbyopia, and astigmatism. Non-conventional errors of the eye include higher-order aberrations, irregular astigmatism, and ocular layer irregularities.
Liquid crystal may be used as a portion of the electro-active optical element as the refractive index of a liquid crystal can be changed by generating an electric field across the liquid crystal. Such an electric field may be generated by applying one or more voltages to electrodes located on both sides of the liquid crystal. Liquid crystal based electro-active optical elements may be particularly well suited for use as a portion of the electro-active optical element since it can provide the required range of optical add powers (plano to +3.00D). This range of optical add powers may be capable of correcting presbyopia in the majority of patients. Finally, liquid crystal can be used to make optics having a diameter greater than 10 mm, which is the minimum size necessary to avoid user discomfort.
A thin layer of liquid crystal (less than 10 μm) may be used to construct the electro-active multi-focal optic. When a thin layer is employed, the shape and size of the electrode(s) may be used to induce certain optical effects within the lens. Electrodes may be “patterned”, which is defined herein as meaning the electrodes may have any size, shape, and arrangement such that with the application of appropriate voltages to the electrodes the optical power created by the liquid crystal is created diffractively. For example, a diffractive grating can be dynamically produced within the liquid crystal by using concentric ring shaped electrodes. Such a grating can produce an optical add power based upon the radii of the rings, the widths of the rings, and the range of voltages separately applied to the different rings. Electrodes may be “pixilated”, which is defined herein as meaning the electrodes may have any size, shape, and arrangement such that each electrode is individually addressable. Furthermore, because the electrodes are individually addressable, any arbitrary pattern of voltages may be applied to the electrodes. For example, pixilated electrodes may be squares or rectangles arranged in a Cartesian array or hexagons arranged in a hexagonal array. Such an array of pixilated electrodes may be used to generate optical add powers by emulating a diffractive, concentric ring electrode structure. Pixilated electrodes may also be used to correct for higher-order aberrations of the eye in a manner similar to that used for correcting atmospheric turbulence effects in ground-based astronomy. This technique, referred to as adaptive optics, can be either refractive or diffractive and is well known in the art.
Alternately, a single continuous electrode may be used alone or with a specialized optical structure known as a surface relief diffractive optic. Such an optic contains a physical substrate which may be designed to have a fixed optical power and/or aberration correction. By applying voltage to the liquid crystal through the electrode, the power/aberration correction can be switched on and off by means of refractive index mismatching and matching, respectively. The required operating voltages for such thin layers of liquid crystal may be quite low, typically less than 5 volts.
A thicker layer of liquid crystal (typically >50 μm) may also be used to construct the electro-active multi-focal optic. For example, a modal lens may be employed to create a refractive optic. Known in the art, modal lenses incorporate a single, continuous low conductivity circular electrode surrounded by, and in electrical contact with, a single high conductivity ring-shaped electrode. Upon application of a single voltage to the high conductivity ring electrode, the low conductivity electrode, essentially a radially symmetric, electrically resistive network, produces a voltage gradient across the layer of liquid crystal, which subsequently induces a refractive index gradient in the liquid crystal. A layer of liquid crystal with a refractive index gradient will function as an electro-active lens and will focus light incident upon it. Regardless of the thickness of the liquid crystal layer, the electrode geometry or the errors of the eye that the electro-active element corrects for, such electro-active spectacle lenses may be fabricated in a manner very similar to liquid crystal displays and in doing so would benefit from the mature parent technology.
An electro-active spectacle lens that provides correction for presbyopia may have to change the optical add power that it provides as a user of the lens looks at objects at different distances. An object that is far away from the user may require less optical add power than an object that is near the user.
Thus, a device is needed which can detect the distance of viewed objects from the user and change the optical power of the electro-active lens such that these objects are properly focused.